Barium and/or strontium glass powder is widely used as a filler in dental restorative resinous compositions because it imparts radiopacity to such compositions. Such resin-based dental filling materials have found limited use, however, for the filling of cavities on the grinding surfaces of molars. The reason for this is that such compositions have been found to have inadequate wearing properties to withstand the stresses which are normal in such areas. Among the factors that contribute to the inadequate wear properties of prior art resinous dental restorative dental compositions are microfractures of the overall composite, and debonding that occurs at the filler/polymer matrix interface. Both of these are most likely to occur during the cyclic loads encountered while chewing in an aqueous environment with attendant modest temperature fluctuations. Inadequate hydrolytic stability appears to contribute to both the microfractures and debonding.
In U.S. patent application Ser. No. 404,262, filed Aug. 2, 1982, now abandoned, entitled "Dental Restorative Compositions Having Improved Mechanical Properties and Hydrolytic Stability", by Dr. N. G. Kumar, and assigned to the same assignee as this application, there is disclosed one approach to the production of dental restorative compositions having improved hydrolytic stability, resistance to debonding at the filler/polymer interface, and resistance to the formation and propagation of microfractures in the composite. One of the important features of the invention disclosed in said application is the use of relatively hydrophobic inorganic fillers. The hydrophobic nature of the fillers that are desired for use in that invention is measured by the amount of water that the filler will absorb when simply exposed to normal ambient atmospheric conditions.
This invention is directed to the provision of barium or strontium glass powder having enhanced hydrophobic properties, and hence, considerably enhanced utility in the preparation of dental restorative resinous compositions.